BOGOTA – An outbreak of the mosquito-borne virus Zika is affecting large parts of Latin America and the Caribbean and spreading quickly through the region.

So far 21 countries and territories in the region have reported cases of Zika, more than double the number only one month ago, according to January 21 figures cited by an expert from the Pan American Health Organisation (PAHO), the regional arm of the WHO.

"The disease is expected to spread across all of Latin America and the Caribbean," Marcos Espinal, head of PAHO/WHO's communicable diseases department, told the Thomson Reuters Foundation in a telephone interview.

The virus was first identified in Uganda in 1947 and was unknown in the Americas until 2014.

The disease is usually relatively mild but the PAHO says it may be linked to cases of brain damage in newborn babies in Brazil.

"There is strong and growing evidence that Zika has a role in this. However, concluding cause and effect is more difficult to prove," PAHO's Espinal said.

Here are some facts about Zika:

* The Zika virus is spread to people through the bite of an infected mosquito, the same mosquito that transmits dengue, chikungunya and yellow fever. There is no vaccine for Zika.

* The Zika virus is usually relatively mild, with symptoms such as skin rash, fever, muscle and joint pain, lasting up to seven days. It is uncommon for people infected with Zika to need hospital treatment.

* In the Americas, there is no evidence that the Zika virus can cause death, PAHO says, but sporadic cases have been reported of more serious complications in people with pre-existing diseases or conditions, causing death.

* Researchers in Brazil and PAHO say there is growing evidence that links Zika to microcephaly, a neurological disorder in which babies are born with smaller than normal heads and brains.

* In north-east Brazil, there has been a marked increase in cases of newborn babies with microcephaly. Brazil's health ministry has said the number of suspected cases of microcephaly in newborns increased by about 360 in the 10 days to January 16 to 3,893.

* Research is under way into the effects of the Zika virus on pregnant women and newborn babies; information about the possible transmission of Zika from infected mothers to babies during pregnancy or childbirth is "very limited", PAHO says.

* Brazil has the highest rate of infection, followed by Colombia. Zika outbreaks have also been reported in Ecuador, El Salvador, Guatemala, Haiti, Honduras, Mexico, Panama, Paraguay, Puerto Rico, Suriname and Venezuela, among other countries.

* Colombia's health ministry says Zika has already infected 13,500 people across the country and there could be as many as 700,000 cases this year.

* Colombia's health ministry has advised women to delay becoming pregnant for six to eight months to avoid possible risks related to the Zika virus.

* Jamaica has not reported any confirmed cases of Zika, but the health ministry has recommended women delay becoming pregnant for the next six to 12 months. El Salvador has advised women to avoid getting pregnant until 2018.

* Earlier this month, the US Centers for Disease Control and Prevention warned pregnant women to avoid travel to 14 countries and territories in Latin America and the Caribbean affected by the virus.

* One in four people infected with Zika develop symptoms and many cases of Zika go undetected, making it difficult to estimate the true scale of the outbreak in the Americas. PAHO says there are no reliable estimates of the number of cases in the region. Based on reports from affected countries, PAHO estimates there are at least 60,000 suspected cases of Zika, though the real figure is thought to be far higher.